Sealed source
Used sealed radioactive sources are considered as waste once the radioactive substances they contain are no longer able to perform their task owing to the decline of their activity. Sealed sources contain a very wide range of radionuclides, including I192, Co60, Cs137, and Sr90 in the short-lived category; Ra226, Ac227, U235, U238, Pu238, Pu239, Pu242, Am241 and Cm244 for long-lived alpha emitters. Sealed sources containing alpha radionuclides are by far the most numerous.